1. Field of the Invention
The present invention relates generally to implantable devices. More particularly, the present invention is directed to a method and apparatus for coating an implantable device having a plurality of depots.
2. Description of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient""s vasculature.
A problem associated with the above procedure includes formation of intimal flaps or torn arterial linings which can collapse and occlude the vessel after the balloon is deflated. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedures which may require another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, an implantable device, such as a stent, may be implanted.
Stents are scaffoldings, usually cylindrical or tubular in shape, which function to physically hold open and, if desired, to expand the wall of the vessel. Typically stents are capable of being compressed, so that they may be inserted through small cavities via catheters, and then expanded to a larger diameter once they are at the desired location.
Although stents are significant innovations in the treatment of occluded vessels, there remains a need for administering therapeutic substances to the treatment site. Systemic administration of the therapeutic substance often produces adverse or toxic side effects for the patient. Local delivery of therapeutic substances, by contrast, provides a smaller overall dosage that is concentrated at a specific treatment site. Local delivery can produce fewer side effects and achieve more effective results.
One technique for the local delivery of therapeutic substances employs medicated coatings on implantable devices. A typical method for medicating an implantable device includes applying a composition containing a polymer, a solvent, and a therapeutic substance to the implantable device using conventional techniques, for example, a dip-coating technique.
A recently developed type of stent includes a plurality of pores, called xe2x80x9cdepotsxe2x80x9d herein, that are formed in the outer surface of the stent. The depots are sized and shaped to contain the composition to ensure that a measured dosage of the composition is delivered with the stent to the specific treatment site. Unfortunlately, When such stents are coated using conventional techniques, undesirable pockets of air can become trapped in the depots. The trapped air reduces the volume available in the depot for holding the composition. The uncertainty regarding the amount of composition loaded in the depots can cause inaccurate dosages being delivered to treatment sites and result in ineffective treatment.
The present invention provides an apparatus and methods of applying a coating to an implantable device (i.e., a device that is designed to be implanted in a human or animal body). Beneficially, the implantable device has depots formed in the outer surface thereof to receive the coating. The present invention provides an effective and economical way for preparing the implantable devices to carry and thus deliver a substantially full dosage of therapeutic substances to a specific treatment site.
An exemplary method within the present invention includes applying a composition including a polymer and a solvent to the surface of the implantable device including the depots. The application of the composition is performed under pressure, which can reduce the surface tension and/or molecular adhesion force of the composition. The reduced surface tension and/or adhesion force allows air pockets formed within the depots to escape while the composition is being driven into the depots.
In another aspect of the present invention, an apparatus is provided for loading an implantable device, which can have at least one depot formed thereon, with a substance. The apparatus includes a mandrel, which supports the implantable device during the loading operation. The apparatus also includes a funnel, which can be submerged in a bath of the substance. The mandrel with the implantable device mounted thereon can be moved within the funnel, which creates a pressure gradient over the implantable device. The pressure gradient reduces a surface tension of the substance, which allows any gas which may have become trapped in the depot during loading to escape.
These and other embodiments of the present invention will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.